Is Husk based on Hydra and is it executing it under the hood?
Husk renders a USD file using a Hydra client, such as Karma or Arnold. The Husk renderer is a stand-alone tool shipped with Houdini which can be used for batch rendering with any Hydra delegate.
When we say the render delegate, does that refer to both the Hydra (viewport) and Husk?
Hydra is an open-source framework to transport live scene graph data to renderers. Hydra is used to transport the scene data to a batch render instead of the Solaris viewport with husk.
Is the Arnold procedural based on Hydra?
The Arnold USD procedural is not based on Hydra at all. The procedural is completely separate and knows nothing about Hydra or render delegates. Kick can render a USD file directly, or an ASS file that uses the USD procedural.